refactor: Simplification in scikit-learn based estimators

[mseeger]

Small changes. Move wrapper code into one file, which is in line with all other wrapper code. Also, simplify imports.
Needed before BO developer tutorial PR goes out.

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

Patch coverage: 89.47% and no project coverage change.

Comparison is base (594b03b) 65.13% compared to head (26f3183) 65.13%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #704   +/-   ##
=======================================
  Coverage   65.13%   65.13%           
=======================================
  Files         421      421           
  Lines       28417    28415    -2     
=======================================
  Hits        18508    18508           
+ Misses       9909     9907    -2     

Impacted Files	Coverage Δ
...edulers/searchers/bayesopt/models/sklearn_model.py	87.09% <85.71%> (ø)
.../schedulers/searchers/bayesopt/sklearn/__init__.py	100.00% <100.00%> (ø)
...rs/searchers/sklearn/sklearn_surrogate_searcher.py	75.00% <100.00%> (ø)
tst/schedulers/bayesopt/test_sklearn_surrogate.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[jgolebiowski]

LGTM, having both in the same file is probably a good idea.